1. Field of the Invention
This invention relates to an improved rubber sealing strip for use in a system for retaining windows on automotive vehicles. More particularly, it relates to an improved rubber seal, which can be used in conjunction with standard urethane retention systems.
2. Description of the Prior Art
It is desirable to have not only one, but two, retention systems to hold automotive windshields in place which simultaneously use the same curable urethane seal. Such a system is disclosed in applicant's co-pending application, Ser. No. 194,883, now U.S. Pat. No. 4,805,363, and discloses how a curable urethane seal can be applied and contained not only on the top of a vehicle window flange, but through the flange, to the other side thereof facing the interior of the vehicle. Unfortunately, even with this double retention system, water leakage occurs between the glass panel and the flange, as well as the outer vehicle flange.
Professionals in the automotive glass replacement industry understand this and, in fact, have, and are, using a third method to add retention and sealing to the glass panel prior to applying it to the vehicle flange, such as when replacing a windshield. Use is made of butyl rubber tape applied continuously around the inside of the glass panel. The tape is supplied as a roll with the butyl tape having a specific configuration. This rubber tape acts as a dam to raise the glass panel above the flange for the addition of curable sealant and actually molds the curable sealant to the inner surface of the glass panel and flange. Such a system is shown in U.S. Pat., No. 4,165,119. In addition, the butyl rubber strip acts as a secondary primary retention device to retain the glass panel to the flange. This is especially important, since aftermarket customers often wish to utilize the vehicle immediately after a new windshield is installed and prior to the urethane fully curing. The butyl rubber is tacky and malleable so that it may be compressed forming not only a dam, but also producing an adhesive force bonding the windshield to the outer surface of the vehicle flange. Using this butyl tape, it is possible for the consumer to actually drive the vehicle away "immediately" after the glass replacement is completed. This is highly desirable, especially in the automotive glass aftermarket.
Using butyl tape, however, in the shape (circular, square, rectangular) as now commercially available to those in the auto glass replacement market, has a major disadvantage in that the actual structural strength of the primary urethane retention system is reduced from that originally present when the automotive glass was installed by the vehicle manufacturer. This is because butyl rubber tape has a retention strength of 35 pounds per square inch, whereas the retention strength of the cured urethane sealant is over 900 pounds per square inch. Thus, every square inch of butyl tape applied to a replacement window in an area that originally had been covered with urethane sealant results in a reduction of structural strength by approximately 870 pounds per square inch. The main problem with the currently available butyl rubber shapes is that when they are placed between the glass panel and the vehicle flange, they expand outwardly covering much of the area between the glass panel and the flange. Therefore, it can be easily understood that even when butyl tape is used by professionals in the auto glass replacement industry, the retention strength of the glass system is not the same as originally produced during the vehicle manufacture, but is significantly less, due to the lost bonding area for the urethane.
It should be noted that approximately six million automotive windshields are replaced every year. One recommended method for replacing these windshields utilizes 3M company butyl rubber sealer, Part No. 08631, which is a square 5/16" on a side. The length of a typical automotive flange or pinchweld is approximately 0.75 inch. Therefore, approximately 50 percent of the bonding area is lost. While 3M recommends a minimum of 1/4" of the flange to be bonded to the window panel with Super Fast Urethane Sealant, Part No. 08609, such a dimension greatly reduces the bonding force between the windpanel and the vehicle flange from that originally present when the vehicle left the factory.
Since the butyl rubber tape utilized in the glass replacement industry is necessary if the vehicle is to be used immediately after window replacement, it has been found that a specific configuration of the butyl tape is advantageous in simultaneously producing a sufficient bond to hold the replacement window on the vehicle until the urethane sealant has cured. This configuration supports the weight of the glass panel and at the same time provides enough initial retention strength to retain the glass panel but without deforming to cover as large an area as the presently available butyl strips. This configuration also allows for a bonding area of urethane sealant between the flange on the vehicle body and the inner side of the window, which is only slightly less than the bonding area utilized during vehicle manufacture.
The use of butyl rubber tape also has several other advantages over a retention system that solely uses urethane. It has been found that the constant resiliency and retention strength of butyl tape seals out acid rain, rain, and humidity. Also, it is less likely to lift off paint from the primer, which commonly occurs because of the torsional bending movement of the glass panels using curable sealant, which is relatively stiff after curing. Thus, the butyl rubber tape is highly advantageous in allowing a glass panel to utilize the resiliency of the butyl tape to absorb and accommodate torsional and bending loads thereon during vehicle operation. When used in combination with urethane, butyl tape can, in fact, reduce the cracking in laminated safety glass from inner surface stone chips that often occur on the outer surface of a vehicle windshield. Because the butyl rubber tape remains resilient, the amplitude of the flexing of the windshield during operation is reduced. This is particularly important on thinner laminated glass, which is now being used in many automotive windsheilds, as compared to the thicker, heavier glass previously used.
The use of butyl tape also reduces what is known in the art as "expansion rust cracking" of glass via the expansion of rust from the vehicle flange to the butyl sealant. Of course, the rust expansion is actually absorbed and accommodated by the resilient butyl tape. Consequently, as the rust bulges outwardly toward the glass window, the force produced is absorbed by the butyl tape.
Heretofore, butyl tape has been configured as an extruded square, an extruded rectangle, or an extrusion having a circular cross section. It has been found that by using the cross section of the present invention, the desirable properties discussed above are produced and enhanced. A bonding area between the glass panel and the vehicle flange being acted upon by the urethane sealant is produced which closely approximates that of the original urethane seal produced during vehicle manufacture. It has been found that the stress related cracking of laminated safety glass panels is reduced when the combination of the urethane sealant and the configuration of butyl tape is reduced, both in the short term and over the life of the vehicle. In addition, other advantages result from the use of butyl tape, such as reduced frequency of water leaks, making it easier to vary the spacing, marginal rust perforation repairs, with or without replacing portions of the flange.